Automatic position-selecting device



J. H PRESSLEY 2 Sheets-Sheet l AUTOMATIC POSITION-SELECTING DEVICE Feb.6, 1940.

Filed sept. 9, 1957 Feb. 6, 1940. 1 H. PRESSLEY 2,188,918

AUTOMATIC POSITION-SELECTING DEVICE Filed Sept. 9, 1937 2 Sheets-Sheet 2Patented Feb. 6, 1940 y UNITED STATES PATENT OFFICE 2,188,918 AUTOMATICPOSITION-SELECTING DEVICE ,Jackson H. Pressley, Abington, Pa., assignorto Philco Radio and Television Corporation, Philli-l delphia, Pa., acorporation of Delaware Application September 9, 1937, Serial No.163,131 14y Claims. (Cl. 172-239) This invention relates to automaticandereratus for controlling the adjustable condenser mote controlpositioning devices lsuch as may be elements of a radio receiver- ACourse adjustemployed to adjust the position of a tuning ele,- mentdevice 2 and a fine adjustment device liefe ment or elements of a radioreceiver. each adapted to control the positioning oi said 5 Theprincipal object of the invention is to proelements. Both of the devices2 and 3 are comvide a novel device which is capable of controllingmutators and are used to direct the flow of curthe adjustment of theshaft of the tuning element rent in the circuit as will be described inmore to stop it accurately in a desired position in redetailhereinafter. In the Specie illustrtion, spense to a simple manual actionsuch as the the radio receiver tuning elements I and the l operation ofa selected push-button. By the rotor of device 2 are mounted on shaft lwhich 10 preferred form of the present Yinvention there is is geared toShaft by reduction gearing l, 7- provided an apparatus which in responseto such The rotor of device 3 iS mounted on shaft 5 which a simpleVmanual eiiort, iirst adjusts the conis driven by motor 8 and in turndrives shaft I. trolled element to an approximate position with- Thus,the rotors of the devices 2 and 3 are rotatin a selected range or zoneand then automati- 8ble With the Shaft 4, and the Position 0f the callyadjusts the said element accurately to a I'OtOl' 0f device 3 iserleleted With the Position 0f desired position within said range. Shaftl.

This apparatus comprises two positioning de- The device 2, asillustrated, comprises a disk 9 vices, one adapted to effect theapproximate ad- 0f insulating materiel, such as Bakelite. mounted`iustment and the other adapted to eiiect the 011 sharit l and Cel'l'ynDeir 0f arcuate cnduc- 20 accurate adjustment of the controlled element.tive Segments l0 and Il and also a conductive scs- Each of these devicescontrols-the effectiveness of ment l2 Which may take the form 0f n ringwith the motive means to drive the controlled element. extensions i3spliced from the' segments I0 und Each of said devices may comprise aplurality of H Electrical COTmectiOn i5 made t0 Segment n stop elements,those of one device corresponding by means 0f the Slip T1118 Il whichiselectlieuy 25 c to various position zones or the controlledeleconnected to segment It, and likewise electrical ment and those ofthe other device correspond- Conneetion iS mede t0 segment Il by means0f ing to particular positions within said zones. 511D ring i5 Which isC0nneeted t0 Segment Il. Means, which may conveniently consist oi aplll- Thebl'ushes l' and I1 Carried by a stator Plate Il 3. rallty ofselector switches in cooperation wtlh an engage or wipe over the sliprings 'Il and I 5, electrically-operable switch, ls provided to ren-TeSPe0tiVe1Y A third brush I9 also carried by der thc first deviceeffective to control c motor the stator plate engages the ring segmentI2. A through o selected contact clement and, at the plurality cibrush-like contact elements 20 are same time, to effect energization ofthe motor, adiustebly mounted in 8 Slet 2| in the stator 36 until thecontrolled element arrives ctlts approxplate, although the elements 20may be Dcrmcv;

imate position, when the electrically-operable nently Xed inPOSitiOn-These eonteet elements switch is actuated to render the first deviceinengage the conductive segments lll and Il and effective and to renderthe other device effective also the extensions I3 of segment l2 duringrcto control the motor tation of the rotor, as will be described further40 'I'he invention maybe more clearly understood hereinafter. Each ofthe contact elements 2l lilyreference to the accompanying drawings, inrepresents a particular range or zone oi movewhich ment of the tuningelements I.

Fig. l is a perspective view of one form of the The device 3, asillustrated, may comprise a apparatus with certain parts broken away forrotatable drum 22 having arcuate conductive M clarity of illustrationments 23 and u se parated by opposed insulating Fg 2 s a demll ew of oneof the selective segments 25 (only one is shown). An end plate push-buton swi c es; 2s i rin 21 and Flc. 3 ls e schematic illustration of theelec- 2s call; toghe com tncal connections of the apparatus ductivesegments 23 and 24,.- Brushes 2! and Il,

Fi 4 is a ra h'c illustration of the manner in Wich the pprtus Operates;and carried by the housing 3i, engage and wipe over Fig. 5 is afragmentary sectional View illustratthe Slip rings 27 and 29,respectively A P11-trent? ing the adjustabley mounting of one of thecontrol 0f brush-like Contact elements 32, eon'espendin elements. innature to the contact elements 2li, are adjust- Referring to Fig. l,there isillustrated an appaably carried in slots I3 in the housing 3l.Each l tact fingers 43, this closes the of the contact elements 32eil'ectively corresponds to a particular position of tuning elements I.

The rotor of device Zhas been illustrated as being a rotatable disk, andthe rotor of device 3 has been illustrated as being a rotatable drum,merely for the sake of illustration. Either of these devices may takeeither of these forms or any other form by which the necessary switchingor commutation may be obtained, as set forth hereinafter.

`'I'he apparatus comprises further a multiplepo1e,fdoublethrow switchingdevice 34, which device comprises a row of stationary contacts 35, asecond row of stationary contacts 38, and mov` able contact fingers 31carried by amovable shaft or rod 38v and adapted to engage either row ofstationary contacts, the fingers 31 being insulated from one another.The rod 38 is connected to an armature 39 lwhich is actuated by eitherof the solenoids 48 and 4I.

A plurality of selective manuals or push-button selector switches,designated generally 42, are provided, one for each position to which itmay be desired to adjust the tuning element I. Each of these switches(see Fig. 2) may comprise spring inger contacts 43, 44 and 45 mounted ona common insulating support 46, and a push-button 41 which is adapted toengage the finger l43 and thus to cause one another. A latch 48 isprovided for each switch, the row of latches being mounted for jointrotary movement on a rotatable rod 49. When one of the push-buttons ispressed inward.v it causes finger 43 to engage nger 44 and causes iinger44 to engage iinger 45, and at the same time the push-button actuatesthe latch 48, releasing any previously depressed push-button. When theactuated push-button is released, the iinger 44 is permitted to moveaway from iinger 45 but the button is latched in and maintains thecontact between ilngers 43 and 44. Thus the contact between ngers 44 and45 is temporary and persists only as longI as the pushbutton is held in,but the contact between fingers 43 and 44 is maintained by the latchingin of the button. When another push-button is pressed inward, any otherpush-button which is in latched position is released by the actuation ofthe latch mechanism. 'I'he purpose of this will be apparent later. f-

The electrical connections of the apparatus, although shown in Fig. 1,are more clearly shown in the diagram of Fig. 3, and the operation ofthe device will be described presently with reference to that figure. Asource of electrical energy, shown as a battery 50, is provided forenergizing the motor 8 and the lsolenoids 48 and 4I. A lamp 5| having ahigh impedance compared to the impedance of motor 8, is included in themotor circuit, and a short-circuiting switch 52 is shunted across thelamp, for a purpose to be described later.

Referring now to Fig. 3, wherein for simplicity the devices 2 and 3 areschematically illustrated as disks or drums with the elements 28 and 32engaging their peripheries, normally switch 52 will be closed and themotor 8 and solenoids 40 and 4I de-energized, the armature 39 beingwithin solenoid 40 so that switch elements 31 are in contact with switchelements 38. Suppose now that a push-button selector switch Xcorresponding to a desired broadcasting station is pressed inward,momentarily closing all three of its con- 44 and 45. It will be seenthat circuit 53 energizing the solenoid i held in engagement by thethree contacts to engage vice 2 is rotated only a 4I. The switch 34 isthus thrown to the left, as viewed in the ligure, closing at contacts35. The releasing of the selector push-button disengages contact iinger45 but the ngers 43 and 44 are the latch mechanism above described.

jI'he closing of switch 34 closes the motor circuit as follows-from thebattery 58 through switch 52, the motor armature, the motor eld winding54. switch 34, conductor 55, segment I Il of device 2, conductor 56,switch 34, conductor 51, contacts 43 and 44, and conductor 58 back to`the battery. The motor rotates shaft 5 clockwise, thus rotating therotor of device 2 counterclockwise until the contact element to whichconductor 56 is connected leaves the segment I0 les` and interrupts themotor circuit. The said contact element, however, engages segment I2 ofdevice 2 and thus energizes the solenoid 40, as will be apparent,causing the switch 34 to throw to the right. The motor is then energizedas follows: from battery 58 through the motor 8 (iield winding 54),switch 34. conductor 59, segment 24 of device 3, the contact element 32corresponding to the above-mentioned contact element of device 2,conductor 69, switch 34, contacts 43 and 44, and conductor 58 back tothe battery. 'Ihe motor 8 again rotates shaft 5 clockwise until thecontact element to which conductor 68 is connected leaves segment 24 andengages the insulating segment 25, thus interrupting the'rnotorcircuit.v Due to the reduction gearing between shafts l4 and 5, therotor of deslight amount by the operation of device- 3. For example, ifthe gear reduction is 16 to l', the maximum possible rotation (180degrees) of the rotor of device 3 during the fine adjustment operationwill rotate the rotor of device 2 only about l1 degrees.

Thus the tuning elements I are adjusted to an approximate positionwithin a certain zone by the action of device 2, and the tuning elementsare then adjusted to an exact position in A that zone by the device 3.To adjust the tuning elements to any other desired station it is simplynecessary to press another push-button corresponding to that station. l

As may be seen from Fig. 3, one end of the iield winding is connectiblethrough switch 34 to segment I8 of device 2, whereas the other end isconnectible to segment II. One of these two segments will be energizedby contact with the element 28 and will cause the motor to rotate insuch a direction as to cause the top of segment I2 to move towards theenergized contact element 28. Likewise, when the second rotor is in use,the two ends of the field winding are connected to segments 23 and 24 ofthe device 3 and one of these segments will be energized by the contactelement 32, causing the motor to rotate in such a direction as to makethe top of insulated Segment 25 rotate towards the energized contactelement 32. Hence, when the pushbutton is depressed, the motor willcause the tuning element to rotate towards the desired position. Thisrotation may of the approximate control 2 to the approximatetuningposition, at which point rotor 2 will relinquish control. This mayoccur either just be fore or just after the desired position is reached.In any event, the ne control 3 will then cause be carried by means themotor to rotate the device directly to the Y positions of the rotors ofdevices 2 and 3 which determine which field winding of the motor B willbe energized. It will be obvious that any number of push-buttons andassociated contact elements 20 and 32 may be provided within the boundsof practicability and the mechanical limitations of the particularapparatus. Moreover, the contact elements and associated circuits cannotinterfere with one another, since the circuit of only one contactelement will be energized at one time.

The operation of the device may be more clearly understood from thefollowing explanation with reference to Fig. 4. Suppose that the tuningelement I may be adjusted through 180 and that it is desired to adjustthe tuning element to any one of six positions within this range.Referring to Fig. 4, these six positions, which may correspond tosixdiierent broadcasting stations, are indicated by the lines A, B, C,etc. The device 3 is adapted to adjust the tuning element I accuratelyto the desired position provided, however, that the tuning element isfirst brought approximately to the desired position. As will beapparent, the device 3 can control the tuning element I only through anangular displacement corresponding to the angular size of the segments23 and 24 divided by the gear ratio between the device 3 and the tuningelements I, and the accuracy with which the device 3 will adjust thepositioning of the tuning element I is similarly determined by thearcuate width of the segment 25 and the gear ratio. If, for example, thesegments 23 and 24 each extends for about 176". and the gear ratio (6-1)is 16 to 1, then the device 3 will bring'the tuning element to thedesired position from any position within the range 11 on either side ofthe desired posif interfere with another.

The device 2 will adjust the tuning element te a position determined bythe angular displacement between the segments I0 and II, and thecontacts 20 should be adjusted so that this region is 4entirely withinthe zone corresponding to the station which it is desired to receive.For example, in Fig. 4 the region g indicated by the double arrow lines,indicates the region within` which the device 2 will first adjust thetuning element and then the device 3 will comploete the tuning oradjusting operation. It is necessary that the region, for example regiong, be entirely within the zone, for example zone a, over which thedevice 3 has control. The region, however, may be anywhere ,within thezone, as forexample, the region l is on one side of position Bn butstill within zone b. Where two stations have overlapping zones, as forexample, stations and F, and Where the region corresponding to anelement 20 of device 2 can be positioned entirely within ,both zones,then a single element 20 may be used with both elements 32 to cause.adjustment of the device to either E or F depending upon which of theelements 32 is employed.

Thus," it will be apparent that the device 3 will control the adjustmentof the tuning element I, provided it is first brought within the zoneover which the device 3 has control, and that the device 2 serves toiirst adjust the tuning element I to a position within that zone afterwhich the device 3 takes control to complete thefinal adjustment.

As indicated above, it is not necessary that there be a contact element20 corresponding to each contact element 32. It is, however, necessarythat there be a section of switch 42 and of switch 34 and a contactelement 32 for each station that it is desired to tune. For example, the

- several contact elements 20 may be permanently fixed so as to dividethe tuning range into a number of iixed regions. Several stations withinany one region may be automatically tuned in by providing a contactelement 32 for each desired station. Each of these different elements 32would then cooperate with the same element 20 to effect the desiredtuning. e In this instance, each element 32 would be connected to adifferent section of switch 34 but the same element 20 would beconnected to each of these several switch sections. This arrangement isshown in Fig. 3 by contact 20a which is connected to cooperate witheither contact 32a or 32h to tune in a station corresponding to either32a. or 32h, both stations being located in the region of contact 20a.

It will further be apparent that it is unnecessary to use the manualpush-button station selector means shown but that, if desired, anautomatic time-controlled mechanism may be used to effect the switchingoperation herein villustratednas performed by the several selectivemanuals 42. Such mechanisms are well known and are to be considered theequivalent in circuit operation of the push-buttons 42.

In practice, it may'be desirable to mount the device 3 on the tuningelement I which is often resiliently mounted. In this case, the device 2may be separately mounted and connected to I through a flexiblecoupling. While the contact elements 20 and 32 may be adjustably mountedin any suitable manner, there is shown in Fig. 5 one form of adjustablemounting wherein the insulating plate 6I, corresponding to either thestator plate I8 or the housing 3|, carries an adjustable sleeve 82within which a springapressed brush 63 is disposed, the brush engag-'ing surface 84 corresponding to the rotor surface of either device 2 ordevice 3. 'Ihe adjustment screw 65 also serves to hold the terminal 66to which electrical connection is made. i

V4The principal purpose of lamp 5I is to enable the manual adjustment ofcontact elements 20 and 32 without causing undesired operation of theapparatus. When the switch 52 is opened,

the high impedance of the lamp is inserted in the motor circuit andprevents operation of the motor. With the radio receiver tuned manuallyto a certain' station, the apparatus may then be adjusted as follows:The push-button to be used for that station is pressed, causing switchv34 to throw to the left as above described. The contact element 20associated with the particular push-button is then moved until the lampis extinguished and the switch u throws te the right. The contactelement 32 associated with the particular push-button is then moveduntil the lamp is again extinguished. 'I'his process is repeated foreachof the push-buttonsv and the lassociated contact elements, it beingunderstood,

of course, that the radio receiver will 'be tuned manually to eachdesired station before the adjustments are made.

It will be apparent that the invention is capable of various modes ofexpression and is applicable to various usages. It is not, therefore, tobe limited by the disclosure herein contained.

I claim:

l. In an apparatus for positioning a movable element, a motor for movingsaid element, a positioning device comprising a plurality of contactsegments engageable by a contact element, a circuit including one ofsaid contact segments and said contact element for controlling theenergization of said motor to move said movable element to a selectedposition range or zone, a second positioning device for controlling theenergization of said motor to move said movable element to a desiredposition within said range, means for connecting either of said devicesto said motor to the exclusion of the other device, manually operablemeans for actuating said connecting means to connect said first deviceto Said motor, and a circuit including another of said contact segmentsand said contact element for actuating said connecting means to connectsaid second 'device to said motor when said movable element has beenmoved to a position Within said range.

2. In a control apparatus for positioning an element, such as a radiotuning element, having a rotatable shaft, a motor for rotating saidshaft, a first positioning commutator constructed and arranged to rotatein correlation with said shaft, a second positioning commutator gearedto said shaftand arranged to have greater angular displacement than saidfirst positioning device, a plurality of segments on cach commutator, acontact for each commutator engageable with said segments, two circuitsthrough said mqtor for causing said motor to rotate in either direction,a switch for connecting segments of one or the other of said commutatorsin circuit with said two motor circuits, and an additional circuit onsaid first commutator for operating Said switch to disconnect said firstcommutator and connect said second commutator to said two motorcircuitsvwhen said shaft is rotated to a selected position.

3. In a control apparatus for positioning a movable element, a firstpositioning device for `controlling the movement of said/element to aselected position range or zone, a second positioning device forcontrolling the movement of said element to a desired position withinsaid range, a linkage between said second positioning device and saidelement for correlating the position of the former vwith respect to thelatter, a selective manual, and switching means controlled by saidselective manual and said first device for rendering said deviceseffective successively to control the movement of said element.

4, In a control apparatus for positioning a rotatable shaft, a motor forrotating said shaft, a first positioning device for controlling therotation of said shaft to a selected position range or zone, saidpositioning device comprising a rotor carrying spaced contacts and aplurality of contactvelements engaging said rotor contacts, said yrotorbeing rotatable by said shaft, a second positioning device forcontrolling the rotation of said shaft to a desired position within saidselected range, said second positioning device comprising arotorcarrying spaced contacts and a plurality of contact elements engagingsaid rotor contacts and each corresponding to a desired position withina position range or zone, a linkage between said second positioningdevice and said lshaft for ,correlating the position of the former withrespect to the latter, means for connecting eitherof said devices tosaid motor to the exclusion of the other device, selector means forenergizing said motor and for actuating said connecting means to rendersaid first device effective to control the rotation of said shaft, andmeans for subsequently actuating said connecting means to render saidfirst positioning device ineffective and to render said secondpositioning device eil'ective to control the rotation of said shaft.

5. In ac control apparatus for positioning an element such as a radiotuning element having a rotatable shaft, a motor for rotating saidshaft, a first positioning device rotatable with said shaft forcontrolling the rotation' of said shaft to a selected position range orzone, a second positioning device rotatable with said shaft forcontrolling the rotationof said shaft to a desired position within saidrange, a iirst circuit including the first positioning device forcontrolling the energization of said motor to cause rotation of saidshaft to said desired position range or zone, a second circuit includingsaid second positioning device for controlling the energization of saidmotor to cause rotation of said shaft to said desired position, a switchfor selectively energizing said circuits and means on said firstpositioning device for actuating said switch to deenergize said iirstcircuit and to energize said second circuit when said shaft has beenrotate to said selected position zone or range.

6. In a control apparatus for positioning a movable element, areversible motor for moving said element, a commutator having a pair ofmain conductive segments and an auxiliary conductive segment, at leastone contact element adapted to engage said segments, a pair of circuitsfor said motor connected respectively to said main segments, manuallyoperable means for connecting said contact element in circuit with saidmotor and an energizing source therefor, whereby said apparatus operatesto position said movable element, a circuit connected to said auxiliarysegment and to said contact element, and switching means controllable bysaid last-named circuit for transferring control of said motor to anauxiliary device. y

'a'. In a control apparatus for. positioninguan element such as a radiotuning element having a rotatable shaft, a motor for rotating saidshaft, a first positioning device rotatable with said shaft forcontrolling the rotation of said shaft to a selected position range orzone, a second positioning device rotatable with said shaft forcontrolling the rotation of said shaft to a desired position within saidrange, a first circuit including the first positioning device forcontrolling the energization of said motor to cause rotation of saidshaft to said desired position range or zone, a second circuit includingsaid second positioning device for controlling the energization of saidmotor to cause rotation of said shaft to said desired position, anelectrically operable switch for energizing either of said circuits, aselector switch having momentarily operable contacts for-energizing saidelectrically operable switch in a direction to energize said firstcircuit, and means on said first positioningxdetice for energizing saidelectrically operable switch in another direction to deenergize thefirst circuit and energize the second circuit when said shaft has beenrotated to said selected position vzone or range.

8. In a control apparatus for positioning a radio tuning element havinga rotatable shaft, a reversible motor for rotating said shaft, anenergizing circuit for said motor, a iirst commutator rotatable withsaid shaft and comprising a pair of main conductive segments and anintermediate conductive segment, a plurality of contact elementsarranged to engage said segments, circuit connections to said segmentsand said contact elements, a second commutator rotatable withAsaid shaftand comprising a pair of conductive segments, a plurality of contactelements arranged to engage said last-mentioned segments, circuitconnections to said segments and said contact elements,electrically-operable switching means constructed and arranged toconnect said vmotor to the pair of segments of either commutator and toconnect the motor `circuit to the associated lcontact elements, aplurality of selector switches for completing the circuit of any one ofthe contact elements, each of said selector switches being constructedand arranged to energize said electrically-operable switching means soas to complete the circuit connections to said first commutator and itsassociated contact elements, and a circuit completable through theintermediate segment of saidfirst commutator for energizing saidelectrically-operable switching means so as to complete the circuitconnections to said second commutator and its associated contactelements.

9. In a control apparatus for positioning a radio tuning element havinga .rotatable shaft, a reversible motor for rotating said shaft, anenergizing circuit'for said motor, a first commutatnr rotatable withsaid shaft and comprising a pair of main conductive segments and anintermediate conductive segment, a plurality of contact elementsarranged to engage said segments, circuit connections to said segmentsand said contact elements, a second commutator rotatable with said shaftand comprising a pair of conductive segments, a plurality of contactelements arranged to engage said last-mentioned segments, circuitconnections to said segments and said contact elements, anelectrically-operable multi-pole double-throw switch arranged to connectsaid motor to the pair of segments of either commutator and to connectthe motor circuit to the associated contact elements, a plurality ofselector switches for completing the circuit oi' any one of the contactelements, each of said selector switches being constructed and arrangedto energize said electrically-operable switch in one direction, and acircuit completable through the intermediate segment of said rstcommutator for energizing said electrically-operable switch in theopposite direction.

10. In a control apparatus for positioning a radio tuning element havinga rotatable shaft, a reversible motor for rotating said shaft, anenergizing circuit for said motor, a iirst commutator rotatable withsaid shaft and comprising a pair of main conductive segments and anintermediate conductive segment, a plurality of contact elementsarranged to engage said segments, circuit connections to said segmentsand said contact elements, a second commutator geared to said shaft soas to rotate to a greater extent than said shaft and comprising a pairof conductive segments, a plurality of adjustable contact elementsarranged to engage said last-mentioned segments, circuit connections tosaid segments and said contact elements, an electrically-operablemultipole double-throw switch arranged to connect said motor to the pairof segments of either commutator and to connect the motor circuit to theassociated contact elements, a plurality of selector switches forcompleting the circuit of any one of the contact elements, each of saidselector switches being constructed and arranged to energize saidelectrically-operable switch in one direction, and a circuit completablethrough the intermediate segment of said first commutator for energizinglsaid electrically-operable switch in the opposite direction. t

l1. In a control apparatus for positioning a rotatable shaft, a motorfor rotating said shaft, a pair of positioning devices each operable bysaid motor, each of said positioning devices comprising circuit makingand breaking elements for -said motor, each of said positioning devicescomprising a plurality of contact segments engageable b y a contactelement for controlling the operation of said motor, the said contactelement representing a position of said shaft,l

means for connecting one of said devices to said motor to the exclusionof the other and vice versa, manually operable means for initiatingoperation of the apparatus and for actuating said connecting means toconnect one of said devices to said motor, and means including a contactsegment on said one device for actuating said connecting means toconnect the other of said devices to said motor.

13. In a control apparatus for positioning a rotatable shaft, a motorfor rotating said shaft,

'a pair of positioning devices each operable by said motor, each of saidpositioning devices comprising circuit making and breaking means,including a plurality of contact elements corresponding respectively topositions of said shaft, for controlling the operation of said motori,means for connecting one of said devices to said motor to the exclusionof the other and vice versa, manually operable means for selecting acontact element corresponding to a desired shaft position and forsimultaneously actuating said connecting means to connect one of saiddevices to said motor, and means controllable by said one device foractuating said connecting means to connect the other of said devices tosaid motor. 14. In a control apparatus for positioning a rotatableshaft, a motor for rotating said shaft, two circuits through said motorfor causing said motor to rotate in either direction, a commutatorincluding two main segments and, an intermediate segment arranged torotate in correlation with said shaft, a second commutator comprisingtwo main 'segments arranged to rotate through a greater angle than saidfirst commutator, a double throw change-over switch, circuits throughone side of said switch and the main segments of the rst commutator tothe two motor circuits; circuits through the other side of said switchand the main segments of said second commutator to the two motorcircuits, an operand to close circuits of'said second commutator, atingmechanism for said switch, a circuit a manually operable switch, and anaouxiliary through the intermediate segment of said nrst circuit throughsaid manually operated switch commutator for energizing said operatingmechafor energizing said operating mechanism to re- 5 nism `to operate.said change-over switch, to tur said change-over switch to normalposition. 5 thereby open al1 circuits of said mst commutator 4 JACKSONH. `ERESSLEY.

